Flow cytometry is a laser-based, biophysical technology where fluorescent molecules coupled to cells are passed through a flow cell and excited by a set of lasers. The fluorescence is collected and separated into different channels with specific detection wavelengths, converted to electrical signals, and analyzed using a computer. By labeling cells with different fluorophores, various distinct cell populations can be resolved. For example, multi-color flow cytometry, such as three color flow cytometry uses fluorophores with different excitation and/or emission wavelengths to differentiate various cell subpopulations within biological samples.
Operationally, an excitation light is delivered to a flow cell by beam-shaping, steering, and guiding optical components. Passing fluorescently labeled cells or particles through the flow cell diffracts the light and excites the labels causing fluorescence. A complex design of multiple-lenses positioned at accurate locations relative to each other and relative to flow cell are employed to collect the fluorescent light and the diffraction light from the particles. The collected light is then split into different channels according to the particular excitation lasers and according to the light wavelength.
In one approach, different fiber optic cables are used to collect the fluorescent/scattered light as excited from different laser sources. Then the light from each fiber optical cable is split into different fluorescent channels. Alternatively, a specially designed objective is used to collect light from particles as they pass through different laser sources and the light is separated into different beams according to which laser source the light was generated and separated into different channels according to different dichroic mirrors.
All such collection optics are expensive to make, difficult to align, and difficult to adjust. Also, for many situations, the light collection efficiency is limited. Furthermore, the collected, split light is conventionally detected and measured with photo-multiplier tubes (PMTs). Whilst PMTs are widely used for flow cytometry applications and other optical measurement situations, they are expensive, bulky in size and complex to use. Therefore, there is a need for improved collection optics that are simple in design, have fewer optic components, have high light-collection efficiency, and have light detection/measurement sensitivity/efficiency.